Phonological opacity poses a big challenge to Optimality Theory all by itself, but it becomes even more recalcitrant when it is conditioned by morphology. For instance, it has been pointed out that nominal inflection in Korean is opaque in certain phonological contexts where verbal inflection is not, which has led previous researchers to posit some noun-specific constraints to deal with the apparently special behavior of nouns. However, this paper shows that the opposite case, where only verbal inflection is opaque, exists, and that just adding category-specific constraints to the OT grammar does not solve the whole morphology-phonology interface puzzle. The proposal in this paper is that all the noun-verb asymmetries can be explained by incorporating morphological structure into OT grammar and that among such models, Stratal OT (Kiparsky 2000) has provided the best solution so far.